The present invention relates generally to anti-terrorist attack measures available to civilians and pertains, more specifically, to a gas mask available to civilians as an emergency measure to counter biological, germ and gas contaminants in the air.
Recent events have prompted the need for the emergency protection of civilians from biological, germ and poisonous gas pollutants in the air, generally designated herein as hazardous air pollutants (HAPs). The most effective methods for controlling HAPs utilize adsorption to remove HAPs from the ambient air. The most common adsorbent employed in such methods is activated carbon. Activated particles in a bed of activated carbon are very porous and have large surface-to-volume ratios. Gases penetrate pore spaces in the bed and contact the large surface areas provided in the bed, where the HAPs adhere so as to be eliminated from the ambient air.
The HAP is held on the activated carbon surface either by physical attractive forces or, in certain cases, depending upon the chemical nature of the molecule and the surface, by chemical forces (chemisorption). In any particular system, both types of adsorption can occur, as well as some intermediate types of adsorption. The adsorption capacity of activated carbon for any given HAP may be represented by an adsorption isotherm that relates the amount of HAP adsorbed (adsorbate) to the equilibrium pressure (concentration) at a constant temperature. Typically the adsorption capacity of activated carbon increases as molecular weight of the HAP increases. Unsaturated compounds are more completely adsorbed than saturated compounds, and cyclical compounds are more easily adsorbed than linearly structured materials.
Adsorption is not unlimited. As the exposed surfaces become increasingly covered with molecules of adsorbate, the rate of adsorption diminishes, reaching zero when saturation of the surface is complete. Thus, the useful life of an activated carbon bed depends upon the concentration of HAP in the air, the amount of gas which passes through the carbon bed, and the total amount of carbon in the bed. A good grade of activated carbon in a bed reaches saturation under high concentrations of HAP when the amount of HAP adsorbed reaches about twenty percent of the weight of carbon in the bed. Lesser grades adsorb down to about five to eight percent of the weight of carbon in the bed.
Adsorption in an activated carbon bed also effectively removes very low concentrations of organics and such beds frequently are specified for air deodorization where the concentration of pollutants often is below five parts-per-million (ppm). Bed depth in such current commercial carbon bed cleaners utilizing granular activated carbon generally is in the range of about 0.5 inch to 3.0 inches, with nominal bed residence times of about 0.025 second to 0.1 second. Carbon systems which are combined with air conditioning filters have a suitable design value of air flow rate of 0.1 ft/second for a bed depth of 0.5 inch.
The properties of different activated carbons can vary widely, and all activated carbons are selective to a certain degree. Activated carbon can be utilized in the form of particles or granules, as well as in the form of activated carbon fibers and carbon-coated fibers. Activated carbon remains as the only reliable physical adsorbing agent for protection against anticipated poison gas attacks. Accordingly, activated carbon is one of the ingredients of civilian and military gas masks and is installed in air conditioning equipment used in connection with underground shelters.
The present invention utilizes the above attributes of activated carbon in a civilian gas mask which can protect personnel against chemical and biological terrorist attacks. As a rule, such attacks take place under indoor conditions, within buildings, shopping malls, subways and the like, where the highest concentration of chemical and biological agents can serve as weapons utilizing a minimum amount of toxic compounds. In such situations, a civilian gas mask need be used for only the relatively short period of time during which personnel can be evacuated to a safe environment. Typically, that duration will be less than one hour.
The present invention provides several objects and advantages, some of which are summarized as follows: Provides a small and compact gas mask which can be stored conveniently in a drawer, or readily carried in a briefcase or coat pocket for emergency use; is available for ready use during a period sufficient to allow a user to escape a contaminated area; is simple in construction and effective in combating biological, germ and poisonous gas contamination; allows full visual effectiveness with enough roominess to avoid claustrophobic reactions, as well as other stressful and emotional effects; enables continuous circulation of fresh, breathable air for promoting well-being; precludes condensation and concomitant impairment of vision by supplying continuously circulated fresh air; provides a simplified construction which is economical to manufacture and easy to use; adapts a universally accepted cap construction for effective and reliable performance readily made available for widespread use.
The above objects and advantages, as well as further objects and advantages, are attained by the present invention which may be described briefly as a civilian anti-terrorist attack gas mask for use by a person as an emergency measure to remove hazardous air pollutants present in air drawn from an ambient atmosphere having an ambient air pressure, and provide the person with suitably breathable air, the gas mask being configured for fitting over the person""s head, above the person""s neck and adjacent the person""s face, the gas mask comprising: a support structure configured for fitting to the person""s head; a brim carried by the support structure for projecting outwardly from the person""s head upon fitting the support structure to the person""s head, the brim having an outside and an inside; a hood carried by the brim and extending from the brim for establishing a chamber having at least a portion contiguous with the person""s face, the chamber being bounded by the hood and the inside of the brim; a passage in the brim, the passage extending from the inside of the brim to the outside of the brim so as to communicate with the chamber and with the ambient atmosphere; an adsorption element in the passage for communicating with the chamber and with the ambient atmosphere; and an impeller assembly for drawing air from the ambient atmosphere into the passage and passing the air through the adsorption element and into the chamber to remove hazardous air pollutants from the air drawn into the passage and deliver an essentially continuous supply of fresh breathable air to the chamber while maintaining an air pressure in the chamber raised above the ambient air pressure.